For the production of corrugated tubing, which is mostly plastic tubing provided with transverse corrugations and more particularly annular or helical corrugations, it is a known practice to mount mold halves in two endless, circulating chains so that following the head of an extruder they are thrust together in the shaping path to give two mutually parallel rows in each of which the mold halves of the respective row constitute hollow molds arranged in a compact train as a travelling mold moving with the tube. These known devices are suitable for the production of small diameters of corrugated tubing, since it is possible to tolerate the disadvantage that the mold halves have to be moved close together along the return paths as well.
If however corrugated tubing with a larger diameter is to be produced, it is necessary to utilize mold halves of suitably large dimensions, whose manufacture is an elaborate process and which involve substantial capital expenditure. In order to make do with the minimum number of mold halves, apparatus has consequently been proposed, in which the mold halves are solely moved together in the shaping path as a train in close succession, whereas they are shunted back separately at a high speed along the return paths so that it is basically only necessary to have one mold half in each return path and accordingly the number of mold halves required for the production of corrugated tubes is reduced to a minimum.
In a device disclosed in the patent publication EP 0 270 694 B for the production of corrugated tubing the conveying device for shunting the mold halves back along the return paths consists of return conveyors composed of two return conveyors, extending along the shaping or working path at a distance from it and of four transverse conveyors which shift the mold halves between the inlet and outlets on the one hand and the return paths in the transverse direction on the other hand. Underneath the mold half path each of the return conveyors possesses an endless traction member comprising a run circulating in the direction of conveying of the respective conveyor. In this respect the traction members bear entrainment means, which at the start of the conveying path come into engagement with the mold halves, entrain the same and at the end of the return path come out of engagement with the mold halves. While this known apparatus ensures a completely satisfactory return movement of the mold halves along the return path, there are however certain difficulties in connection with the transverse shifting of the mold halves by means of transverse conveyor, since such conveyor must ensure a fitting together of the mold halves without any jamming and skew running in the inlet and a correspondingly free drawing apart of the mold halves at the outlet.
In the case of an apparatus disclosed in the patent publication EP 0 007 556 B of the type initially mentioned problems in connection with the fitting together of the mold halves without skew running and jamming together of the mold halves at the inlet of the shaping path and the drawing apart of the mold halves at the outlet of the working path are solved by designing the gripping arms of the carriage in the form of pivotally mounted pivot arms, which, owing to having an appropriate control means for the pivot movement render it possible for a pivotal component to be combined with the translatory carriage movement with the result that the mold halves, when moving into the shaping path at the inlet thereof and when leaving the shaping path at the outlet thereof, are able to be guided along the desired oblique and curved cam tracks. This known device does however suffer from the disadvantage of requiring elaborate control means in order to combine the pivotal movement of the gripping arms with the movement in translation of the carriages to get the desired guide paths for the mold halves and from the further disadvantage that the bearing means for the pivot arms have to be very massively dimensioned for them to be able to transmit the necessary moments in view of the substantial weight of the pivot arms. Furthermore for the known pivot arm design additional measures have to be taken to prevent the same from exerting a twisting effect on the mold halves as the same are moved out of the outlet and are shunted back to the inlet.
In the case of the known device the pivot arms are hence designed in the form of parallel link systems, which so pivot the mold halves that the same remain parallel to themselves during pivotal movements. The known device therefore as well calls for an elaborate and expensive design owing to the form of the pivot arms in the form of parallel link arrays.